1. Field of the Invention
The present invention relates to exposure apparatuses used in manufacturing processes of devices, such as semiconductor and liquid crystal devices, and having high controllability of stages, and to device-manufacturing methods performed using such exposure apparatuses.
2. Description of the Related Art
In related art, when devices such as semiconductor or liquid crystal devices are to be manufactured, a projection-type exposure apparatus is used. Specifically, in such an exposure apparatus of a projection type, a pattern drawn on a reticle by photolithography is de-magnified and projected by a projection optical system, and the pattern is then transferred onto a wafer.
In order to perform an exposure process with high precision, the reticle is held by a reticle stage and moves together with the reticle stage.
If the exposure apparatus is of a scanning type, the reticle stage needs to move by a long stroke along one of its axes. There have been proposed technologies in which an interferometer is used to enhance the mobility of the reticle stage that moves by a long stroke along the one axis.
One example of such a technology is proposed in Japanese Patent Laid-Open No. 2001-345254, which discloses a compact stage device that has a laser interferometer for achieving high-precision measurement and that can move with high precision.
A reticle stage described in Japanese Patent Laid-Open No. 2001-345254 will be described below with reference to FIGS. 7A and 7B. In detail, the position of a reticle stage 110 in a Y-axis direction is measured on the basis of measurement light Y1 or Y2 from a laser interferometer. The position of the reticle stage 110 in an X-axis direction is measured on the basis of measurement light X1. The position of the reticle stage 110 in a Z-axis direction is measured on the basis of measurement light Z. For the position measurement in the Z-axis direction, a mirror 119e is provided on the reticle stage 110, and a mirror 111d is provided above the reticle stage 110. The measurement light from the laser interferometer is reflected orthogonally upward by the mirror 119e and is subsequently reflected by the mirror 111d provided above the reticle stage 110. The measurement light is reflected again by the mirror 119e so as to be guided to the laser interferometer.
Providing the mirrors 119e and 111d allows for high-precision measurement of the position of the reticle stage 110 in the Z-axis direction.
In order to measure the position of the reticle stage 110 in the Z-axis direction in the related art described above, the mirror 111d above the reticle stage 110 needs to extend over the stroke range. In this case, a supporting structure for supporting the mirror 111d is necessary. However, since an optical system for guiding exposure light to the reticle is disposed above the reticle stage 110, there is not enough space for such a structure.
Furthermore, because the position of the reticle stage 110 is determined on the basis of a projection optical system, it is desirable that the mirror 111d be supported by a supporting structure that supports the projection optical system.
However, there are serious design limitations in providing such a supporting structure that supports the projection optical system above the reticle stage 110. In other words, it is desirable that a projection optical system be similarly disposed below the reticle stage 110 and that the space between the reticle and the projection optical system be reduced to enhance the optical performance of the exposure apparatus. However, if the laser interferometer is disposed directly below the reticle stage 110, there is not enough space for the projection optical system and the like.